This invention relates generally to pollution cleanup and more particularly concerns a method and apparatus for remedial recovery of hydrocarbons accumulated atop the ground water table as a result of spills, storage tank leaks and dumping.
The method and apparatus disclosed herein employs an improved submersible pneumatic pump adapted to recover gasoline, hydrocarbons and other lighter than water pollutants from the top of a subterranean water table. Hydrocarbons such as gasoline and oil are frequently spilled, leaked or dumped into the soil. These hydrocarbons soak into the ground, ultimately collecting atop the ground water table. Layers of hydrocarbon, as thick as sixteen feet deep, have been found atop ground water tables at or adjacent to refinery sites, gas stations and hydrocarbon storage facilities.
The present invention employs a submersible pneumatic pump to skim hydrocarbons from the surface of a water table. Prior art attempts to recover floating hydrocarbons have been costly, inefficient and tend to recover excessive quantities of ground water. The method and apparatus of the present invention assures the recovery of hydrocarbon pollutant without the accompanying production of significant amounts of ground water.
Prior art attempts to efficiently remove contaminates from atop the ground water table have been frustrated by failure to take into account a variety of conceptual, methodological and geological factors.
First, the recovery of pollutants from atop the ground water table normally involves very shallow recovery wells. Very frequently, the upper portions of the hydrocarbon layer are only a short distance beneath the surface. The soft and frequently sandy characteristics of the surrounding geological formation are very different from the characteristics of hard rock geological formations surrounding deeper wells.
Second, water tends to move more quickly through these shallow formations than does the pollutant, whose movement through a formation is dependent upon relatively small hydrostatic forces.
Third, efficient remedial hydrocarbon recovery requires that the rate of recovery not exceed the rate of hydrocarbon movement through the geological formation.
Fourth, efficient remedial hydrocarbon recovery requires that the collection situs be within the narrow layer of hydrocarbon and above the water table.
In contrast to the conventional aims of enhanced recovery (both in terms of quantity and rate) associated with oil and water wells, pollution cleanups require slow controlled recovery in order to accommodate the characteristics particular to the product and geological formation involved.
Prior art hydrocarbon pollution cleanup systems have typically failed to accommodate the tendency of hydrocarbons to move through a formation more slowly than water. Consequently, these systems produce large quantities of ground water and frequently so saturate the geological formation surrounding the collection site with water as to impede the influx of hydrocarbon to the collection site. The method and apparatus of the present invention employs a submersible pump situated above the ground water table within the hydrocarbon layer; the action of the pump being directly regulated by the influx of hydrocarbon to the collection site.